1. Field of the Invention
The present invention relates to a coated base fabric for airbags and a polyamide (PA) reproduced material made of a waste material of the coated base fabric.
2. Description of the Related Art
Airbag devices for protecting occupants are mounted in vehicles. Examples of base fabrics for airbags incorporated in the airbag devices include the following two types: a cloth (uncoated base fabric) obtained by weaving (normally plain weaving) PA fiber yarns (for example, nylon 66); and a coated cloth (coated base fabric) obtained by forming an elastomer coating film on one surface or both surfaces of the cloth.
All vehicles should be installed with airbag devices, which include one for a front passenger seat, as standard equipment. Recently, a waste material of a base fabric for airbags (including scraps generated in cutting the base fabric, hereinafter, the same) is generated in a large amount.
A request for recycling (reusing) the above waste material of the base fabric as a PA reproduced material from the viewpoint of the formation of a recycling society has increased.
Since the uncoated base fabric, which is made of only the PA fiber yarn, is easily reproduced, the recycling of the uncoated base fabric has been put into practice.
However, as shown in Patent Documents 1 to 3, the coated base fabric obtained by coating a silicone rubber or a silicone resin on a cloth made of a PA fiber yarn has become major.
Patent Document 1 describes “a chloroprene rubber, a chlorosulfonated rubber and a silicone rubber” as a coating film material of an elastomer coating film in paragraph 0013. Patent Document 2 describes “a silicone resin, a polyurethane resin and a polyamide-based resin” in paragraph 0061. Patent Document 3 describes “chloroprene, chlorosulfonated olefin, a silicone rubber and a polyamide-based elastomer . . . .” Each of Patent Documents teaches that “a silicone rubber (a silicone resin)” has excellent heat resistance in Examples or “the silicone rubber (a silicone resin)” is particularly preferable.
Before the filing of the present application, it was considered common knowledge for those skilled in the art that “a material of an elastomer coating film must be a rubber or resin having excellent heat resistance equivalent or superior to that of a cloth.”
In Patent Documents 2 and 3, the PA elastomer is also exemplified as the forming material of the elastomer coating film. However, the present inventors imagine that the recycling of the PA elastomer is not naturally predetermined, and a PA elastomer having a low melting point of the present invention is not predetermined from the above description. However, when such a PA elastomer having a high melting point is used, the present inventors assume that the flexibility of the base fabric is difficult to secure while securing required air tightness (low airflow amount) of the base fabric.
Since a request for securing quicker and more highly precise initial restrictiveness as the function of the airbag in order to protect the occupants has increased particularly in recent years, higher air tightness has been increasingly required from the viewpoint of the development characteristics of the airbag. On the other hand, the required flexibility (low impact resilience) is also an indispensable requirement from the viewpoint of the folding quality of the airbag and the above development characteristics of the airbag.
Generally, common knowledge of those skilled in the art is that a trade-off request exists between the above high air tightness and flexibility of the coated base fabric. That is, it is necessary to form a relatively thick-walled coating film in order to secure high air tightness. However, the thickened coating film increases the mass of the airbag. Alternatively, the thickened coating film relatively increases the impact resilience, and thereby the flexibility of the airbag is difficult to secure. In addition, the thickened coating film has an adverse effect on the folding quality.
Patent Documents 4 and 5 teach the same PA elastomer (soft PA) as that of the present invention as the coating film material of the elastomer coating film.
That is, claim 1 of Patent Document 4 teaches that “a base fabric for airbags composed of a synthetic fiber yarn, wherein the base fabric is impregnated with a water-soluble or water-dispersible synthetic resin, and the synthetic resin is formed into a film having 0.3 mm thickness and the resin has tensile elongation of 200% or more and strength of 5 MPa or less in 200% tension when carrying out a tensile test under conditions of a 35 mm distance between chucks and a 300 mm/min tensile speed using a tensile tester.” Claim 2 of Patent Document 4 teaches that “the synthetic resin is selected from a polyurethane resin, an acrylic resin, a polyester resin and a polyamide resin.” Furthermore, paragraph 0028 of Patent Document 4 teaches “TORESIN (trade name, manufactured by Teikoku Chemical Industry Co., Ltd., N-methoxymethylated nylon)” as a preferred example as soft PA.
However, the present inventors assume that predetermined air tightness is difficult to secure in the soft PA (PA elastomer). This is because according to the article description (Nagase ChemteX Corporation issue) of “TORESIN,” “TORESIN F-30K,” which has water vapor permeability (g·cm/cm2·s·cmHg×1012: 38° C., 24 h, 25 μm film thickness) of “3060,” shows a value close to “3800” of “regenerated cellulose” and has water vapor permeability of 20 times or more of “160” of “nylon 6.”
And, “TORESIN,” which is alcohol-soluble nylon, is predetermined as a solution type coating material. Therefore, it is assumed that resin forming a coating film intrudes into the clearance of the cloth and to secure the flexibility of the coated base fabric become difficult.
Further, Patent Document 5 teaches a dried coating film formed on one surface of a cloth made of nylon 66, the coating film made of a PA elastomer (a block copolymer containing a soft segment as amino-modified polyether). However, referring to the drying temperature of the coating film in the document, the drying finish temperature is 110° C. in Example 1 (a paragraph 0018). It is difficult to presume that the PA elastomer is melted and the coating film is fused on the cloth.    Patent Document 1: Japanese Published Patent Application No. H6-81274 A    Patent Document 2: Japanese Published Patent Application No. 2004-176221 A    Patent Document 3: Japanese Published Patent Application No. 2006-249655 A    Patent Document 4: Japanese Published Patent Application No. 2004-218138 A    Patent Document 5: Japanese Published Patent Application No. 2008-13897 A